## 4.2.1 MU on Windows
Click “**This PC**” to check “**Properties**” to know whether your system is 32 bit or 64 bit.
The system type can be seen: 64-bit
⚠️ **Note:** MU no longer supports 32-bit Windows. The currently recommended version is MU 1.2.0. So please update to this version on your computer.
### 4.2.1.1 Download MU
[Click to download the MU on Windows](https://codewith.mu/en/download).
### 4.2.1.2 Install MU
**Step 1-Run the installation program:**
Find the installer you just downloaded (it may be in your download folder) and click to open it.
A warning message will be popped up on Windows Defender. Click “**More info**”.
The message will change to provide more information about the installer, and display a “**Run anyway**” button. Click the button.
**Step 2-License agreement:**
Check the license, tick the accept box, and click “**Install**”.
**Step 3-Installation:**
When MU is installed on your computer, it takes a few seconds.
**Step 4-Complete:**
After installed, click “**Finish**”.
**Step 5-Start the MU:**
Directly click MU to enter it, or search it to open. At the first start, this may take a few seconds.
MU main interface:
[How to install MU on windows?](https://codewith.mu/en/howto/1.2/install_windows)
## 4.2.2 MU on MacOSX
### 4.2.2.1 Download MU
[Click to download the MU on MacOS](https://codewith.mu/en/download).
### 4.2.2.2 Install MU
[How to install MU on MacOS?](https://codewith.mu/en/howto/1.2/install_macos)
## 4.2.3 MU on Linux
### 4.2.3.1 Download MU
[Click to download the MU on Linux](https://codewith.mu/en/download).
### 4.2.3.2 Install MU
[How to install MU on Linux?](https://codewith.mu/en/howto/1.2/install_linux)
## 4.3 Settings and Toolbar
⚠️ **Note:** Here we demonstrate how to use it on Windows system (as a reference for MacOSX and Linux).
Set “**Mode**” to BBC micro:bit when used for the first time.
Open MU, click the “**Mode**” to select “**BBC micro：bit**”, and then click “**OK**”.
Please refer to the [official introduction and tutorials for the MU operations](https://codewith.mu/en/tutorials/1.1/start).
For more tutorials about MU, please visit: [https://codewith.mu/en/tutorials/](https://codewith.mu/en/tutorials/)
## 4.4 Import Library on MU
⚠️ **Note:** Before importing a library file, you need to upload a .py code (empty code is also acceptable) to the micro:bit board . Here, we import an empty code.
1\. Connect the micro:bit board to the computer via a micro USB cable, open the Mu editor, click “**New**” to create a .py code(empty), and then click the “**Flash**” to upload the empty code to the board.
In this tutorial, OLED display and XHT11 temperature and humidity sensor require libraries. So we need to import “**oled_ssd1306\.py**” and “**DHT11\.py**”.
The default directory for saving files in MU is “**mu_code**”, which is located in the root directory of the user directory.
Reference: [https://codewith.mu/en/tutorials/1.0/files](https://codewith.mu/en/tutorials/1.0/files).
**2\. Import libraries:**
2.1\. Double-click to open the C drive of your computer. Search for "**mu_code**” on the C drive of your computer and find the "**mu_code**” folder.
2.2\. Open “**mu_code**”.
2.3\. Copy and paste the library files “**oled_ssd1306\.py**” and “**DHT11\.py**” from the “**Libraries**” folder to the “**mu_code**” directory at the following path.
2.4\. In “**mu_code**”, you then can see “**oled_ssd1306\.py**” and “**DHT11\.py**”:
2.5\. Open MU and click “**Files**”. Drag “**DHT11\.py**” to the micro:bit.
2.6\. And you can see “**DHT11\.py**” in the left box:
2.7\. Similarly, import “**oled_ssd1306\.py**”.
2.8\. After adding the library files “**oled_ssd1306\.py**” and “**DHT11\.py**” , click the “**Files**” button again.
⚠️ **Note: After importing libraries, click “**Flash**” to download the .py code file to micro:bit board. If the on-board 5*5 LED matrix shows the error, you need to re-load these libraries.**
## 4.5 Load Code to MU
Here we take “**heartbeat\.py**” in the folder “**Heart beat**” as an example.
**Method one:**
Open MU and click “**Load**” to open the file you need.
Loaded:
**Method two:**
There is a much simpler way to load code.
Open MU and click  , select “**heartbeat\.py**” and drag it into MU:
Loaded:
## 4.6 Download Code to Mciro:bit
⚠️ **Note:** After uploading a code to the micro:bit board, the original content will be overwritten, so it needs to be re-imported the next time you use it.
Connect micro:bit board to computer via USB cable.
Click “**Flash**” to load the code to micro:bit board.
After downloading, **power on via micro USB cable**, and the on-board 5×5 LED matrix shows  and  in a loop.
⚠️ **Note:** If the code includes errors, it can also be downloaded to micro: bit, but it does not work properly.
For example, when sleep() is wrongly written to sleeps(), click “**Flash**” to download the code to the board, and the 5×5 LED matrix may show error message and incorrect line number.
Click “**REPL**” and the reset button (**on the back of micro:bit board, not A/B button**), and the error message will be displayed in the REPL.
Click “**REPL**” again to close it. After correcting the error, click “**Flash**” to re-download the code.
After writing the code, click “**Check**” to ensure the code is correct. For instance, click “**Check**” and the MU will point out errors.
Modify the code according to the prompt, and then click “**Check**” to ensure the code is now correct.
For more tutorials of MU, please visit: [https://codewith.mu/en/tutorials/](https://codewith.mu/en/tutorials/)